Hydrobromic acid, preparation properties

It is common practice to refer to the molecular species HX and also the pure (anhydrous) compounds as hydrogen halides, and to call their aqueous solutions hydrohalic acids. Both the anhydrous compounds and their aqueous solutions will be considered in this section. HCl and hydrochloric acid are major industrial chemicals and there is also a substantial production of HF and hydrofluoric acid. HBr and hydrobromic acid are made on a much smaller scale and there seems to be little industrial demand for HI and hydriodic acid. It will be convenient to discuss first the preparation and industrial uses of the compounds and then to consider their molecular and bulk physical properties. The chemical reactivity of the anhydrous compounds and their acidic aqueous solutions will then be reviewed, and the section concludes with a discussion of the anhydrous compounds as nonaqueous solvents. 

Properties of Hydrobromic Acid. 1, See how the prepared hydro-bromic acid acts on a metal (magnesium or zinc) and on calcium carbonate. 

As methods of preparation, only the first three need be considered. It was decided not to try the direct action of bromine upon naphthalene, owing to the necessity of stirring the solid naphthalene and of collecting the hydrogen bromide gas the latter difficulty is also presented when carbon disulfide is used, and the objectionable properties of this solvent make its use further unfavorable. The third method, in which a suspension of naphthalene in alkaline hypobromite solution is treated with hydrochloric acid in aqueous solution, was found to give satisfactory results in so far as the yield of a-bromonaphthalene is concerned (though it was no better than with the method above described), but it presented considerable difficulties in the recovery of the hydrobromic acid. 

RPR 200,735 is a weak base. Its conjugate acid has a pA"a of 5.3. Only strong acids are able to form a stable salt with RPR 200,735. Investigated acids include hydrochloric acid, hydrobromic acid, and methanesulfonic acid (Table 13.2). The methanesulfonate salt was found to be superior to the other salts in all aspects water solubility, hygroscopy (absorption of moisture from air), and rate of dissolving. Furthermore, the flow properties of the methanesulfonate salt facilitated capsule and tablet preparation. 

A given alcohol is treated with 25 percent excess of aqueous (48 per cent) hydrobromic acid together with sulfuric acid. The mixture is refluxed in order to convert the alcohol as completely as possible into the corresponding bromide, and the latter is then removed from the reaction mixture by distillation. Slight variations from this procedure depend upon the physical and chemical properties of the alcohol used, or of the bromide formed in the reaction. For example, in the preparations of ethyl and allyl bromides, the reaction mixture is not refluxed because of the volatility of the former compound, and because of the chemical reactivity of the latter in the preparation of wo amyl bromide, too large a proportion of sulfuric acid may produce appreciable decomposition while halides of high molecular weight, because of their low volatility, are separated from the reaction mixture mechanically, instead of by distillation. 

Properties Olive-green, brown, or black crystals. Soluble in water insoluble in alcohol. Prepared by action of hydrobromic acid on iridium trihydroxide. 

In the course of this work the preparation of tricyclic compound 87 was accomplished by treatment of the mixture of 96 and 97 with concentrated hydrobromic acid. Chromatography of the mixture gave a racemate whose properties in solution were identical with those of 87. This conversion confirms the structural assignments made on the spectroscopic evidence and discussed in the previous section. 

---